1. Field of the Invention
The present invention relates to a display apparatus for projecting an image.
2. Description of the Related Art
Projectors receive an image signal from a personal computer and project an image depending on the image signal onto a screen. The image projected from the projector onto the screen generally has an aspect ratio of 4:3. The aspect ratio refers to the ratio of the horizontal size to vertical size of the image.
Some personal computers (hereinafter referred to as an “ordinary PC”) have a display aspect ratio of 4:3 and others (hereinafter referred to as “wide PC”) have a display aspect ratio of 16:9, 16:10, or 15:9. These computers employ image signals corresponding to the aspect ratios of their displays.
When a projector having an aspect ratio of 4:3 receives an image signal from an ordinary PC having a display aspect ratio of 4:3, the projector projects a distortion-free image that is identical to the image displayed on the display screen of the ordinary PC.
However, when a projector having an aspect ratio of 4:3 receives an image signal from a wide PC having a display aspect ratio of 16:9, the projector projects an image at the aspect ratio of 4:3 though the image should be displayed at the aspect ratio of 16:9. Therefore, the image projected from the projector onto the screen is distorted, i.e., it is compressed horizontally and expanded vertically, and is not easily viewable.
JP-A No. 2003-348496 (hereinafter referred to as “Patent Document 1”) discloses a projector for making screen-projected images easily viewable. Specifically, the projector disclosed in Patent Document 1 identifies the aspect ratio of an image frame based on the image signal sent from a PC. If the image from the PC is a high-definition image, then the projector identifies the aspect ratio of the image as 16:9. If the image from the PC is an ordinary image, then the projector identifies the aspect ratio of the image as 4:3. The projector projects the image at the identified aspect ratio onto the screen.
The projector disclosed in Patent Document 1 thus identifies the aspect ratio based on the image signal. However, it is difficult for the projector to properly identify the aspect ratios of image signals which are similar to each other, e.g., the aspect ratios of 15:9, 16:9, and 16:10. If the projector fails to identify the aspect ratio of an image, then it cannot project the image at its own aspect ratio, but projects an image that is not easily viewable.